Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Synaptic plasma membranes, synaptic junctions, and postsynaptic densities have been isolated from rat brain, the proteins resolved by polyacrylamide gel electrophoresis, and the glycoproteins identified. The synaptic junction is composed of a spectrum of polypeptides which range in Mr from 13,000 to 250,000. The overall pattern is similar to synaptic plasma memranes; however, the relative proportions of the polypeptides are distinctive. The postsynaptic density fraction consists primarily of one band with an Mr of 52,000. Polypeptides with an Mr of 55,000, and another five of higher Mr, make up the remaining protein. The polypeptides of the postsynaptic density fraction must be reduced with mercaptoethanol in order to permeate the polyacrylamide gel. Therefore, postsynaptic density proteins are cross-linked by disulfide bonds into supramacromolecular aggregates. Glycoproteins which bind concanavalin A were identified in synaptic junctions by studying the binding of 123I-concanavalin A directly to the polypeptides resolved on the polyacrylamide gels. Only four bands, each with an Mr greater than 95,000, bind concanavalin A. In contrast, the pattern of concanavalin A-binding polypeptides in synaptic plasma membranes is distinctive and more complex. In the postsynaptic density fraction, most of the concanavalin A binding occurs to a glyco-component which migrates at the dye front. These data, together with previous cytochemical data using concanavalin A-ferritin conjugates, indicate a limited and select group of high Mr concanavalin A glycoproteins resides within the synaptic cleft of asymmetric type synapses. Whereas a select group of polypeptides bind concanavalin A, all polypeptides resolved in the synaptic junction fraction are glycoproteins and contain galactosyl or galactosyl-like residues, since they label with tritiated borohydride following galactose oxidase treatment. This suggests that the carbohydrate composition of individual glycoproteins is different.
 ...
PMID:Identification of glycoproteins and proteins at synapses in the central nervous system. 83 52

To expand the electron microscopist's options in localization and visualization, a new and general staining technique has been tested. The avidin-biotin complex serves as a coupling between the electron-dense marker, ferritin, and points of interest in biological samples. When specific cellular components are tagged with biotin, those components may be visualized with ferritin-linked avidin. Because of the remarkably strong affinity of avidin and biotin (characterized by an association constant of 10(15) M(-1)), the staining is rapid and stable. The preparation of ferritin-avidin conjugate is described, and examples are presented of the application of this complex to biotin-tagged membranes. The ghosts of Acholeplasma laidlawii have been treated with biotinyl-N-hydroxysuccinimide ester to label protein amino groups. Erythrocyte membrane oligosaccharides have been oxidized by periodate or by galactose oxidase, and the resulting aldehydes labeled with biotin hydrazide. The avidin-biotin complex in electron microscopy seems especially appropriate for seqential staining procedures, as well as for visualization of reaction sites of biotin-labeled, low-molecular-weight reagents.
 ...
PMID:Use of the avidin-biotin complex for specific staining of biological membranes in electron microscopy. 413 15

Plasma membrane vesicles of rat myometrium were prepared in media containing 240 mM sucrose. The vesicles were exposed to isotonic, hypertonic, and hypotonic sucrose concentrations, fixed, sectioned, and studied using the electron microscope. The vesicles fixed in isotonic media were circular in appearance. Vesicles fixed in hypertonic media were distorted and showed a reduced volume to surface ratio consistent with the hypothesis that greater than 80% of the vesicles were osmotically active to sucrose. Cationized ferritin binding studies and Ca binding and release studies were also consistent with this finding. Exposure to hypotonic media also yielded membranes with distorted profiles indicating that they had been ruptured. [3H]Sucrose trapping experiments revealed that the vesicles had an internal volume of 1.20-1.44 mL/g protein. Hypotonic shock treatment reduced this intravesicular volume to 0.20-0.28 mL/g protein. The hypotonic shock treatment also led to enhanced galactose oxidase catalyzed Na3B3H4 labelling of the membranes and to increased K+-activated ouabain-sensitive p-nitrophenyl phosphatase activity. The enhancement was the same (55 +/- 10%) in the various membrane preparations for both the parameters. The data are interpreted to conclude that the rat myometrium plasma membrane vesicles consisted of 20% broken vesicles and equal proportions of intact vesicles of inside-out and rightside-out orientations.
 ...
PMID:Smooth muscle membrane vesicle orientation: a study on intactness and sidedness of rat myometrium plasma membrane vesicles. 625 66

The avidin-biotin complex was used for the selective ultrastructural labeling of terminal cell surface galactosyl residues. Rabbit bone marrow cells were treated with the enzyme galactose oxidase in the presence of biotin hydrazide. Subsequent treatment with ferritin-avidin conjugates enabled the electron microscopic visualization of terminal membrane-based galactose and/or N-acetylgalactosamine on these cells. All stages of erythroid development were characterized by high levels of exposed cell surface galactose, whereas all leukoid cells in the same preparations were virtually unlabeled by the above method. Modulations in the distribution of these surface determinants during differentiation and maturation of rabbit erythroid cells were found to concur in inverse fashion with respect to that of terminal sialic acids. Neuraminidase treatment, before the above labeling procedure, resulted in the exposure of additional galactosyl residues on the surface of all bone marrow cell types. The results indicate that a galactose-bearing glycoconjugate(s) may comprise an erythroid-specific membrane constituent of rabbit bone marrow cells. The high density of galactose on the surface of even the earliest erythroid precursors may eventually enable the identification and isolation of a stem cell, which already contains the erythroid-specific galactoconjugate(s). The results suggest that variations in the spectrum of cell surface carbohydrates may serve as recognition signals in the complex set of intercellular interactions which occur during the development and maturation of the erythrocyte. The occurrence of similar but species-specific variations in the complement of surface heterosaccharides during erythroid development of humans and other mammals supports this contention.
 ...
PMID:Cell-type-related segregation of surface galactosyl-containing components at an early developmental stage in hemopoietic bone marrow cells in the rabbit. 682 46

The suitability of isolated central nerve myelin preparations for probe labelling studies was assessed and the accessibility of galactosyl ceramides in myelin to galactose oxidase and sodium periodate was determined. Isolated myelin preparations present a uniform external membrane surface to added probes because lamellae in the myelin sheath separate at their external apposition surfaces exclusively during isolation. The cytoplasmic apposition remains intact in isolated myelin. Cationised ferritin can gain access along external apposition regions of inner lamellae in multilamellar fragments of isolated myelin, indicating that proteins and lipids on the external membrane surface will be accessible to probes. Over 50% of the total galactosyl ceramides of myelin are accessible to galactose oxidase attack; hydroxy fatty acid- and nonhydroxy fatty acid-containing cerebrosides are equally attacked. Sodium periodate attacks over 90% of the galactosyl ceramides in isolated myelin at 20 degrees C and electron micrographs of the periodate-treated myelin reveal changes at the external apposition only. Galactosyl ceramides in vesicles of myelin lipid vesicles are not so readily attacked by periodate. The disposition of galactosyl ceramides in the myelin lamellae is discussed.
 ...
PMID:Accessibility of galactosyl ceramides to probe reagents in central nervous system myelin. 745